What was Tesla's first U.S. patent issued in 1886 for?

Tesla’s first U.S. patent issued in 1886 was for a commutator for dynamo electric machines. U.S. Patent No. 334,823 was granted on January 26, 1886, for an improvement intended to reduce sparking and wear in dynamo commutators.

A commutator is the rotating switching device used in many direct-current machines. It reverses current in the armature coils at the proper moment, allowing a motor to keep turning or a generator to deliver current in one direction. Tesla’s design added insulating and protective features around the commutator bars and brushes.

The date wording matters. Tesla also filed a dynamo-electric-machine application in January 1886, but that patent was not granted until 1887. The commutator patent is therefore identified as his first U.S. patent issued in 1886. It predates his best-known alternating-current motor patents, which were granted in May 1888.